First, a couple of examples of what not to do...
Pretty self-explanatory why this is no good! It may as well not be there.
This is better, but still not great in Perth's strong winds. The tree can still slide back and forth along the strapping, chafing the bark and possibly even dashing the branches against the stakes. People do this because they over-estimate how much movement a tree needs to trigger its trunk strengthening process. Answer: not this much! I suspect they also use this product because of its durability but the welfare of the tree is the more important consideration.
This is the way to go: separate ties pulling in opposite directions (there are three stakes here but it works just as well with two). There's no way this tree can hit the stakes and there's no chance of chafing either. But the tree can still move - not a lot, but enough to trigger it's natural trunk strengthening process. I've seen and tried a lot of ways to tie a tree in 30 years but still haven't found a better method than this.